Process and device for producing granulates by fluidized bed spray granulation

Abstract

This invention relates to a process for the production of granulates by fluidized bed spray granulation and to a device for this purpose. Liquid starting materials may be converted into granulates by fluidized bed spray granulation. In order to ensure elevated material throughput, numerous nozzles, which are moreover susceptible to plugging and encrustation, must be installed. The disadvantages of known processes may be overcome according to the invention by arranging at least two spray nozzles at least partially directed towards each other in such a manner and the quantity of spray is adjusted in such a manner that their spray jets collide within the fluidized bed and substantially no liquid strike-through occurs onto a surface delimiting the fluidized bed or out of the fluidized bed. The spray jets of two spray nozzles directed towards each other collide frontally or enclose an angle of less than 180°; the angle is preferably between 150° and 180°. The device according to the invention comprises a flow channel (1) with laterally arranged spray nozzles (8), wherein in each case two exactly opposing or staggered spray nozzles are oriented in such a manner that the spray jets collide within the fluidized bed. Sodium percarbonate production is exemplfied.

We claim: 
     
       1. A process for producing solid granulates from at least one starting material by fluidized bed spray granulation, comprising: performing said spray granulation in a flow channel, the bottom of which is arranged as a fluidizing base plate;   spraying at least one liquid starting material from at least one pair of spray nozzles onto particles in a fluidized bed;   wherein each of said spray nozzles is at least a two-fluid nozzle for dispensing at least two fluids;   wherein one fluid of said at least two fluids is a gas for atomizing fluid droplets of said liquid starting material;   wherein the nozzles of said at least one pair of spray nozzles are at least partially directed toward each other;   wherein said at least one pair of spray nozzles are arranged laterally along said flow channel;   wherein spray jets from said spray nozzles directed toward each other collide and form an angle of from 150° to 180° wherein line connecting two spray nozzles facing each other and the spray jets emitted therefrom form an angle relative to horizontal of from 0° to +15° C.,   wherein the quantity of spray is adjusted so that the spray jets collide within said fluidized bed and substantially no liquid strike-through occurs onto a surface delimiting the fluidized bed or out of the fluidized bed, and   wherein said liquid starting material is converted into solid granulates.   
     
     
       2. The process according to claim 1, wherein a total momentum of each colliding spray jet is substantially equal. 
     
     
       3. The process according to claim 1, wherein said at least one pair of spray nozzles are arranged laterally and arranged opposite each other along said flow channel within a depth of said fluidized bed. 
     
     
       4. The process according to claim 1, further comprising: pneumatically classifying said granulates during or after discharging said granulates; and   returning said granulates which are smaller than a predetermined size to said fluidized bed.   
     
     
       5. The process according to claim 1, wherein said flow channel is subdivided into two or more chambers, and   wherein a separating wall between said chambers takes the form of a weir having a horizontal slot both at the bottom and in the depth of the expanded fluidized bed.   
     
     
       6. The process according to claim 1, wherein said spray nozzles are three-fluid nozzles in which said sprayed liquid starting material is contacted outside of said nozzle.   
     
     
       7. A device for producing solid granulates from at least one liquid starting material by fluidized bed spray granulation, comprising: a flow channel, the bottom of which is arranged as a fluidizing base plate;   at least one pair of spray nozzles, arranged laterally along said flow channels and at least partially directed toward each other, each nozzle of which is at least a two-fluid nozzle for dispensing at least two fluids, in which one of said fluids is said at least one liquid starting material to be sprayed onto particles in a fluidized bed, and   in which the other of said fluids is a gas for atomizing fluid droplets of said at least one liquid starting material;     wherein spray jets from said spray nozzles collide and form an angle of from 150° to 180°, and wherein a line connecting said at least one pair of spray nozzles directed toward each other and the spray jets emitted therefrom form an angle relative to horizontal of from 0° to 15°;   wherein a quantity of material comprising said spray jets is adjusted so that the spray jets collide within said fluidized bed such that substantially no liquid strike-through occurs onto a surface delimiting said fluidized bed, or outside of said fluidized bed; and   wherein said at least one liquid starting material contacts said particles to form said solid granulates.   
     
     
       8. The device according to claim 7, further comprising: a granulate discharge means having an integrated pneumatic classifier, and   a means for returning particles smaller than a predetermined size to said fluidized bed.   
     
     
       9. The device according to claim 7, wherein said flow channel comprises two or more chambers with separating walls therebetween which form a combined underflow and overflow weir. 
     
     
       10. A process of producing granulates by fluidized bed spray granulation using the apparatus according to claim 7. 
     
     
       11. The process according to claim 10, wherein said particles in said fluidized bed comprise nuclei having an average grain diameter of 0.1 mm which comprise about 2% of the resulting solid granulate. 
     
     
       12. The process according to claim 10, wherein a volumetric flow rate of materials flowing from said nozzles is from 30-145 l/h. 
     
     
       13. The process according to claim 10, wherein said gas is pressurized. 
     
     
       14. The process according to claim 10, wherein said solid granulates are relatively dense and substantially spherical.